CN111826620A - Gradient Coatings for Glass Molding Moulds that Inhibit Element Diffusion and Anti-Stick - Google Patents

Abstract

The invention belongs to the technical field of glass mold coatings only containing inorganic materials, and particularly relates to a gradient coating for a glass mold pressing mold, which can inhibit element diffusion and prevent adhesion. The glass mold pressing gradient coating comprises a Cr bonding layer bonded with a matrix, a CrN intermediate transition layer and Cr_xW_yN_(1‑x‑y)Surface layer, and 0.15<x<0.4，0.2≤y<0.45. The gradient coating has excellent crack propagation inhibiting performance and anti-adhesion performance.

Description

Gradient Coatings for Glass Molding Moulds that Inhibit Element Diffusion and Anti-Stick

technical field

The invention belongs to the technical field of glass mold coatings containing only inorganic materials, and in particular relates to a gradient coating for glass molding molds that inhibits element diffusion and prevents sticking.

Background technique

Glass precision molding is a high-efficiency and environmentally friendly advanced optical component manufacturing technology, which has developed rapidly in recent years ("Research Progress in Glass Precision Molding", Gong Feng et al., Optical Precision Engineering, 2018 Vol. 26 No. 6 , p. 1380, abstract, published on June 30, 2018). Optical glass molding technology utilizes the continuous and reversible thermal processing properties of glass in the transformation from molten state to solid state. Near the transition temperature T _g of glass, under oxygen-free conditions, the glass and mold are heated and pressurized, and the glass and mold are heated and pressurized at one time. Optical glass molding. Because the optical glass molding method abandons the traditional rough grinding, fine grinding, polishing and centering edging and other processes, it can be directly formed at one time, which greatly saves materials, time, equipment and labor, and can mold optical components with complex shapes. Especially in the manufacture of aspherical optical glass parts and small and micro optical components, it has broad application prospects ("Optical Glass Molding Technology", Wang Lirong, Science and Technology Communication, No. 7, 2012, p. 105, published in 2012. July 23). Therefore, the optical glass molding technology is especially suitable for mass production of various high-precision medium and small-diameter lenses with special structures, especially those optical glass components that are difficult to achieve with traditional processing methods, such as small-diameter thin lenses, high-order aspherical lenses, Microlens arrays, diffractive optical elements and freeform optical elements, etc. Since optical glass molding technology can produce precise aspheric or free-form surface optical components in large quantities, the application of aspheric glass optical components is promoted ("Precision molding technology in optical glass manufacturing research", Wu Cheng, Market Weekly: Theoretical Research , No. 2, 2012, p. 111, published on June 1, 2012).

The service life and surface quality of the mold have always limited the development of glass precision molding technology. The main reason is that in the molding process of glass products, the mold frequently contacts with high-temperature molten glass, resulting in synergistic effects such as oxidation reaction, thermal fatigue, dynamic wear, and adhesion ("Development and Application of Glass Mold Materials", Wei Yuping). et al, Mechanical Design and Manufacturing, No.3, 2008, p. 201, published on March 31, 2008; "Development and Application of New Glass Mould Materials", Xiao Ming, Glass and Enamel, Vol. 34, 2006 Issue 2, page 19, published on April 30, 2006). In addition, the quality of the mold surface is closely related to the molding quality of the glass element. Therefore, glass molding dies need to have excellent high temperature resistance, oxidation resistance, adhesion resistance, thermal fatigue resistance, corrosion resistance, and wear resistance.

Therefore, in order to prolong the service life of the mold and improve the quality of optical components, the method of coating the surface of the mold should be used to improve the high temperature resistance, oxidation resistance, adhesion resistance, thermal fatigue resistance, corrosion resistance, wear resistance, etc. performance. However, due to the lack of the use of mold coatings, the processing methods used in my country are still dominated by traditional CNC cutting, grinding, polishing and other methods. It is urgent to find a glass mold coating that inhibits element diffusion and prevents adhesion.

SUMMARY OF THE INVENTION

In view of this, an object of the present invention is to provide a gradient coating for a glass molding die, which is excellent in inhibiting element diffusion and anti-adhesion performance, and has a low cost.

For achieving the above object, the technical scheme of the present invention is:

Gradient coating for glass molding die, including Cr bonding layer linked with substrate, CrN intermediate transition layer and surface Cr _x W _y N _(1-xy) layer, and 0.15<x<0.4, 0.2≤y<0.45.

Further, the thickness of the Cr bonding layer is 50-100 nm, the thickness of the CrN intermediate transition layer is 150-300 nm, and the thickness of the surface Cr _x W _y N _(1-xy) layer is 1300-1500 nm.

Further, the high temperature wetting angle of the gradient coating at 1000°C is 125°.

Further, the substrate is a tungsten carbide mold doped with 8% Co, in mass percentage.

The second object of the present invention is to protect the preparation method of the gradient coating of the glass molding die, comprising the following steps:

A. Under the atmosphere of vacuum and inert gas, the substrate to be deposited and the target are cleaned by sputtering;

B. Under inert gas and vacuum atmosphere, use Cr target and W target to sequentially deposit Cr bonding layer, CrN intermediate transition layer and Cr _x W _y N _(1-xy) layer on the surface of the substrate to be deposited processed in step A.

Further, the inert gas is argon, nitrogen or a mixture of the two.

Further, in step A, the flow rate is 100-180sccm, the vacuum degree during sputtering is 0.4-0.5Pa, the substrate is preheated to 200-400°C, preferably 300-400°C, the deposition bias is -30--70V, and the substrate is sputtered. The sputtering cleaning time is 30-120 minutes, preferably 60-120 minutes, and the target sputtering cleaning time is 1-5 minutes, preferably 2-5 minutes.

Further, in step B, the deposition conditions of the Cr bonding layer are as follows: the vacuum degree of the vacuum chamber substrate is 3×10 ^-3 -6×10 ^-3 Pa, the working gas is argon, and the vacuum degree of the reaction chamber is 0.4-0.5Pa during the deposition process , the deposition bias voltage is -30--70V, the Cr target power is 3-6kW, the deposition temperature is 300-400°C, and the deposition time is 2-5 minutes.

Further, in step B, the deposition conditions of the CrN intermediate transition layer are as follows: the working gas is a mixed gas of argon and nitrogen, the vacuum degree during sputtering is 0.4-0.5Pa, the deposition bias is -30--70V, and the Cr target power is 3-6kW, deposition temperature is 300-400℃, deposition time is 20-40 minutes.

Further, in step B, the deposition conditions of the Cr _x W _y N _(1-xy) layer are as follows: the working gas is a mixed gas of argon and nitrogen, the vacuum degree during sputtering is 0.4-0.5Pa, and the deposition bias is -30~ -70V, Cr target power is 3-6kW, W target power is 4-6kW, deposition temperature is 300-400°C, and deposition time is 60-100 minutes.

Further, the deposition is plasma enhanced magnetron sputtering.

Further, before step A, the following steps are also included:

(1) Polish the substrate to be deposited;

(2) ultrasonically clean the polished substrate to be deposited in deionized water and/or acetone and/or ethanol.

Furthermore, when the target is sputtered and cleaned, the target is shielded by a backing plate.

The third object of the present invention is to protect the application of the glass molding mold gradient coating in the preparation of glass molding molds.

The object of the present invention is also to protect a glass molding mold, the mold comprises a glass molding mold gradient coating, and the gradient coating includes a Cr bonding layer linked with a substrate, a CrN intermediate transition layer and a surface Cr _x W _y N _{( 1-xy)} layer, and 0.15<x<0.4, 0.2≤y<0.45.

Further, the substrate is a tungsten carbide mold doped with 8% Co, in mass percentage.

The beneficial effects of the present invention are:

The surface morphology of the gradient coating of the present invention presents cauliflower-like clusters of different sizes, and the surface presents defects such as fine cracks and holes. From the cross section of the coating, it can be observed that the growth mode of the coating is a columnar crystal structure; the layers are tightly bonded.

The gradient coating of the present invention exhibits excellent mechanical properties and meets the hardness usage standard for glass molded coatings.

The coating of the invention has low surface roughness, excellent surface quality, and meets the application requirements of the surface quality of precision glass molding coating.

The gradient coating of the present invention has excellent high temperature resistance and anti-adhesion properties. The surface of the glass and mold coating of the gradient coating after hot pressing has no obvious change, no discoloration reaction of the glass body, no bubble generation, and no adhesion phenomenon on the surface. , the part of the coating surface in contact with the glass did not peel off.

The gradient coating of the present invention has excellent high temperature resistance and anti-adhesion properties.

The gradient coating of the present invention is excellent in suppressing crack propagation.

The gradient coating of the present invention is low cost.

Description of drawings

Fig. 1 is the structural representation of the gradient coating of the present invention;

Fig. 2 is the SEM surface and cross-sectional view of the gradient coating obtained in Example 1, wherein, 2A is the surface view of the coating, and 2B is the cross-sectional view of the coating;

Fig. 3 is the hardness test result of the gradient coating obtained in Example 1;

Fig. 4 is the surface roughness test result of the gradient coating obtained in Example 1;

Fig. 5 is the gradient coating and glass surface topography diagram of the gradient coating obtained in Example 1 after molding;

Fig. 6 is a graph of the detection results (i.e., energy spectrum) of the surface elements of the gradient coating obtained in Example 1;

Fig. 7 is the phase structure detection result diagram of the gradient coating obtained in Example 1;

Fig. 8 is the high temperature wetting performance test result diagram of the gradient coating obtained in Example 1;

Fig. 9 is a graph showing the crack growth inhibition test result of the gradient coating; wherein, 9A is the crack growth inhibition test result graph of the gradient coating obtained in Example 1; 9B is the crack growth inhibition test result of the gradient coating obtained in Comparative Example 1 9C is a graph of the detection result of inhibiting crack growth of the coating prepared in Comparative Example 2.

Detailed ways

The cited embodiments are used to better illustrate the content of the present invention, but the content of the present invention is not limited to the cited embodiments. Therefore, those skilled in the art make non-essential improvements and adjustments to the embodiments according to the above-mentioned contents of the invention, which still belong to the protection scope of the present invention.

Example 1

Glass molding mold gradient coating, its specific preparation steps are:

(1) Pre-plating treatment

The substrate to be deposited (tungsten carbide mold doped with 8% Co, in mass percentage) was mechanically ground and polished, and then cleaned by ultrasonic vibration in deionized water, acetone, and ethanol solution for 20 minutes each, and the samples were placed in an oven after cleaning. Dry at 80℃ for 30min;

(2) Sputter cleaning

The pre-plated substrate to be deposited is loaded into a vacuum chamber, and the vacuum chamber is pre-evacuated, the vacuum degree of the substrate is 5×10 ^-3 Pa, and the vacuum chamber is heated to 300°C during this process. High-purity argon gas (purity>99.99%, known from the outer packaging) was introduced to clean the substrate and target by ion sputtering etching, the flow rate was 120sccm, the vacuum degree during sputtering was 0.4Pa, and the deposition bias was -70V. The substrate sputtering cleaning time is 60 minutes, and the target sputtering cleaning time is 5 minutes; when the target is sputtered and cleaned, the target is covered with a liner;

(3) Deposition of Cr bonding layer

A plasma-enhanced magnetron sputtering system is used to pre-deposit a Cr bonding layer on the substrate to be deposited; the vacuum degree of the vacuum chamber substrate is 5×10 ^-3 Pa, and the working gas is high-purity argon (purity>99.99%, known from the outer packaging) , the target used is a high-purity Cr target (purity > 99.9%, known from the outer packaging), the vacuum degree during sputtering is 0.4Pa, the deposition bias is -30V, the Cr target power is 5kW, and the deposition temperature is 300 ℃, The deposition time was 5 minutes.

(4) Deposition of CrN intermediate transition layer

Plasma-enhanced magnetron sputtering system is used to re-deposit a CrN transition layer on the surface of the above-deposited Cr bonding layer substrate; the working gas is high-purity argon (purity>99.99%, known from the outer packaging), high-purity nitrogen (purity>99.99% , known from the outer packaging) mixed gas, the target used is a high-purity Cr target (purity > 99.9%, known from the outer packaging), the vacuum degree is kept at 0.4Pa during sputtering, the deposition bias is -30V, and the power of the Cr target is was 5kW, the deposition temperature was 300°C, and the deposition time was 20 minutes.

(5) Deposition of Cr _x W _y N _(1-xy) surface layer

Plasma-enhanced magnetron sputtering system was used to re-deposit a Cr _x W _y N _(1-xy) surface layer on the surface of the above-deposited Cr bonding layer and CrN transition layer. The working gas was high-purity argon (purity >99.99%, with Known from the outer packaging), high-purity nitrogen (purity>99.99%, known from the outer packaging) mixed gas, the target materials used are a high-purity Cr target (purity of 99.9%, known from the outer packaging) and a high-purity W target (purity is 99.6%, known from the outer packaging), the vacuum degree is kept at 0.4Pa during sputtering, the deposition bias is -30V, the Cr target power is 3kW, the W target power is 4kW, the deposition temperature is 300°C, and the deposition time is 60 minutes .

Comparative Example 1

Glass molding mold gradient coating, its specific preparation steps are:

(1) Pre-plating treatment

The substrate to be deposited (tungsten carbide mold doped with 8% Co, in mass percentage) was mechanically ground and polished, and then cleaned by ultrasonic vibration in deionized water, acetone, and ethanol solution for 20 minutes each, and the samples were placed in an oven after cleaning. Dry at 80℃ for 30min;

(2) Sputter cleaning

The pre-plated substrate to be deposited is loaded into a vacuum chamber, and the vacuum chamber is pre-evacuated, the vacuum degree of the substrate is 5×10 ^-3 Pa, and the vacuum chamber is heated to 300°C during this process. High-purity argon gas (purity>99.99%, known from the outer packaging) was introduced to clean the substrate and target by ion sputtering etching, the flow rate was 120sccm, the vacuum degree during sputtering was 0.4Pa, and the deposition bias was -70V. The substrate sputtering cleaning time is 60 minutes, and the target sputtering cleaning time is 5 minutes; when the target is sputtered and cleaned, the target is covered with a liner;

(3) Deposition of Cr bonding layer

A magnetron sputtering system was used to pre-deposit a Cr bonding layer on the substrate to be deposited; the vacuum degree of the vacuum chamber substrate was 5×10 ^-3 Pa, and the working gas was high-purity argon (purity>99.99%, known from the outer packaging), and the The target material is a high-purity Cr target (purity>99.9%, known from the outer packaging), the vacuum degree during sputtering is 0.4Pa, the deposition bias is -30V, the Cr target power is 5kW, the deposition temperature is 300℃, and the deposition time is for 5 minutes.

(4) Deposition of Cr _x W _y N _(1-xy) surface layer

A magnetron sputtering system was used to redeposit a Cr _x W _y N _(1-xy) surface layer on the surface of the above-deposited Cr bonding layer substrate; Pure nitrogen (purity>99.99%, known from the outer packaging) mixed gas, the target materials used are a high-purity Cr target (purity 99.9%, known from the outer packaging) and a high-purity W target (purity 99.6%, known from the outer packaging) Packaging information), keep the vacuum degree at 0.4Pa during sputtering, the deposition bias voltage is -30V, the Cr target power is 3kW, the W target power is 4kW, the deposition temperature is 300°C, and the deposition time is 60 minutes.

Comparative Example 2

Glass molding die coating, its specific preparation steps are:

(1) Pre-plating treatment

The substrate to be deposited (tungsten carbide mold doped with 8% Co, in mass percentage) was mechanically ground and polished, and then cleaned by ultrasonic vibration in deionized water, acetone, and ethanol solution for 20 minutes each, and the samples were placed in an oven after cleaning. Dry at 80℃ for 30min;

(2) Sputter cleaning

The pre-plated substrate to be deposited is loaded into a vacuum chamber, and the vacuum chamber is pre-evacuated, the vacuum degree of the substrate is 5×10 ^-3 Pa, and the vacuum chamber is heated to 300°C during this process. High-purity argon gas (purity>99.99%, known from the outer packaging) was introduced to clean the substrate and target by ion sputtering etching, the flow rate was 120sccm, the vacuum degree during sputtering was 0.4Pa, and the deposition bias was -70V. The substrate sputtering cleaning time is 60 minutes, and the target sputtering cleaning time is 5 minutes; when the target is sputtered and cleaned, the target is covered with a liner;

(3) Deposition of Cr _x W _y N _(1-xy) layer

A magnetron sputtering system is used to deposit a Cr _x W _y N _(1-xy) surface layer on the substrate to be deposited; the working gas is high-purity argon (purity>99.99%, known from the outer packaging), high-purity nitrogen (purity >99.99%, known from the outer packaging) mixed gas, the target materials used are a high-purity Cr target (99.9% purity, known from the outer packaging) and a high-purity W target (purity 99.6%, known from the outer packaging), During sputtering, the vacuum degree was kept at 0.4Pa, the deposition bias was -30V, the Cr target power was 4kW, the W target power was 4kW, the deposition temperature was 300°C, and the deposition time was 60 minutes.

Performance testing

The coating obtained in Example 1 is subjected to performance tests such as coating surface and cross-sectional morphology, hardness, surface roughness, molding, coating surface elements, coating phase structure, high temperature wetting performance, and the results are shown in Figure 2- As shown in Figure 8;

At the same time, the gradient coatings prepared in Example 1 and Comparative Example 1 and the coatings prepared in Comparative Example 2 were tested for their performance in inhibiting crack growth. The results are shown in Figure 9, of which Figure 9A is the gradient coating prepared in Example 1. Coating, Figure 9B is the gradient coating prepared by Comparative Example 1, and Figure 9C is the coating prepared by Comparative Example 2;

Wherein, Fig. 2 is the SEM surface and sectional view of the gradient coating obtained in Example 1, wherein, 2A is the surface view of the coating, 2B is the sectional view of the coating; Fig. 3 is the hardness test result, wherein the abscissa is the indentation Depth, the ordinate is the indentation load; Figure 4 is the surface roughness test result; Figure 5 is the molding test result; Figure 6 is the surface element detection result of the gradient coating (ie, energy spectrum); Phase structure test result chart; Figure 8 is a high temperature wettability test result chart;

Among them, the hardness detection method is: using a nano-indenter to test, the test mode is continuous stiffness method (CSM), wherein, in order to exclude the influence of the matrix on the measurement results, the nano-indentation depth is set to 100nm, in order to ensure the accuracy of the data Reliable, choose 5 different areas on the sample, and take the average value of the obtained hardness and elastic modulus;

The detection method of surface roughness is: use atomic force microscope to test, and the test sample area is 2 × 2 μm;

The detection method of molding is as follows: using self-designed optical aspheric glass molding equipment (application number: CN201710124489.7; publication number: CN106946441A), molding BK7 optical glass; wherein, the molding pressure is 0.5kN, and the molding temperature is 650 ℃; observe the surface morphology and color of the mold coating and BK7 glass after molding;

The detection method of the coating surface elements is: qualitative analysis of the coating surface elements by using the X-ray energy dispersive spectrometer (EDS) of the Field Emission Scanning Electron Microscope (FESEM);

The detection method of the phase structure is as follows: X-ray diffractometer (XRD) is used for detection, in order to avoid the influence of the matrix factor, the crystal structure of the coating is analyzed by means of small angle diffraction;

The testing method of high temperature wetting performance is as follows: the high temperature wetting experiment is carried out at 1000 ℃ by the drop method through the pipe, the vacuum degree is 5×10 ^-3 Pa, and the glass material is BK7 optical glass;

The testing method for inhibiting crack growth performance is as follows: use a Rockwell hardness tester to test the ability of the coating to be tested to inhibit crack growth, and apply a load of 60N to the coating using a diamond indenter with a cone angle of 120°. The surface of the coating after pressing was observed using a super-depth of field microscope.

It can be seen from Figure 2 that the surface morphology of the gradient coating prepared in Example 1 is cauliflower-like clusters of different sizes, and the surface presents fine cracks and other defects. From the cross section of the coating, it can be observed that the growth mode of the coating is a columnar crystal structure, the thickness of the Cr layer is 96 nm, the thickness of the CrN layer is 297 nm, and the thickness of the Cr _x W _y N _(1-xy) layer is 1375 nm; the layers are tightly bonded.

It can be seen from Figure 3 that the hardness of the gradient coating prepared in Example 1 is 16GPa. Thus, it is proved that the gradient coating of the present invention exhibits excellent mechanical properties and meets the use standard of glass molding coating.

It can be seen from FIG. 4 that the surface roughness of the gradient coating prepared in Example 1 is 4 nm, showing excellent surface quality, and can be used for precision glass molding coating.

It can be seen from 5 that the surface of the glass and mold coating of the gradient coating prepared in Example 1 after hot pressing has no obvious change, the glass body has no discoloration reaction, no bubbles are generated, the surface does not stick, and the coating surface is in contact with the glass. part did not peel off. It is thus proved that the gradient coating of the present invention has excellent high temperature resistance and anti-adhesion properties.

It can be seen from FIG. 6 that the main elements on the surface of the gradient coating prepared in Example 1 are Cr element, W element and N element.

It can be seen from Figure 7 that the surface layer of the gradient coating prepared in Example 1 has obvious CrN phase, the main crystal orientations are (111), (200), (220), (311), (222) orientation, and the surface layer The mass percentage of Cr element is 35%, the mass percentage of W element is 20%, and the mass percentage of N element is 45%.

It can be seen from Figure 8 that the gradient coating prepared in Example 1 did not spread on the surface of the molten optical glass and the gradient coating when the ambient temperature was 1000 degrees and the vacuum degree was 5 × 10 ^-3 Pa, and the surface of the molten glass and the coating did not spread. The high temperature contact angle is 125°. This proves that the gradient coating of the present invention has excellent high temperature resistance and anti-adhesion properties.

It can be seen from FIG. 9 that, compared with the gradient coating of Comparative Example 1 and the coating of Comparative Example 2, the number of cracks in the gradient coating of Example 1 is significantly reduced. It is thus proved that the gradient coating of the present invention has significantly improved performance in inhibiting crack propagation.

In addition, it should be understood that although this specification is described in terms of embodiments, not each embodiment only includes an independent technical solution, and this description in the specification is only for the sake of clarity, and those skilled in the art should take the specification as a whole , the technical solutions in each embodiment can also be appropriately combined to form other implementations that can be understood by those skilled in the art.

Claims (10)

1. Gradient coating for glass molding die, characterized in that it comprises a Cr bonding layer, a CrN intermediate transition layer and a Cr _x W _y N _(1-xy) surface layer bonded to the substrate, and 0.15<x<0.4, 0.2≤ y<0.45. 2. The glass molding die gradient coating according to claim 1, wherein the thickness of the Cr bonding layer is 50-100nm, the thickness of the CrN intermediate transition layer is 150-300nm, and the surface Cr _x W _y N _{(1 -xy)} layer thickness of 1300-1500 nm. 3 . The gradient coating for glass molding molds according to claim 1 or 2 , wherein the gradient coating has a high temperature wetting angle of 125° at 1000° C. 4 . 4. the preparation method of the glass molding die gradient coating described in any one of claim 1-3, is characterized in that, comprises the following steps: A. Under the atmosphere of vacuum and inert gas, the substrate to be deposited and the target are cleaned by sputtering; B. Under inert gas and vacuum atmosphere, use Cr target and W target to sequentially deposit Cr bonding layer, CrN intermediate transition layer and Cr _x W _y N _(1-xy) layer on the surface of the substrate to be deposited processed in step A. 5 . The preparation method according to claim 4 , wherein the inert gas is argon, nitrogen or a mixture of the two. 6 . 6. The preparation method according to claim 4 or 5, characterized in that, in step A, the flow rate is 100-180sccm, the vacuum degree during sputtering is 0.4-0.5Pa, the substrate is preheated to 200-400°C, and the deposition bias is applied. It is -30 to -70V, the substrate sputtering cleaning time is 30-120 minutes, and the target sputtering cleaning time is 1-5 minutes. 7. The preparation method according to claim 4 or 5, wherein in step B, the deposition conditions of the Cr bonding layer are: the vacuum degree of the vacuum chamber substrate is 3×10 ^-3 to 6×10 ^-3 Pa, and the working gas is Argon gas, the vacuum degree of the reaction chamber is 0.4-0.5Pa, the deposition bias is -30--70V, the Cr target power is 3-6kW, the deposition temperature is 300-400°C, and the deposition time is 2-5 minutes. 8. according to the described preparation method of claim 4,5 or 6, it is characterized in that: in step B, the deposition condition of CrN intermediate transition layer is: working gas is argon, nitrogen mixed gas, and vacuum degree is 0.4- during sputtering 0.5Pa, the deposition bias voltage is -30--70V, the Cr target power is 3-6kW, the deposition temperature is 300-400°C, and the deposition time is 20-40 minutes. 9. The application of the gradient coating for a glass molding die according to any one of claims 1 to 3 in the preparation of a glass molding die. 10. A glass molding die, characterized in that it comprises a glass molding die gradient coating, the gradient coating comprising a Cr bonding layer, a CrN intermediate transition layer and a Cr _x W _y N _(1-xy) surface layer bonded to a substrate , and 0.15<x<0.4, 0.2≤y<0.45.

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